1. Field of the Invention
The present invention relates to a rotor of a rotary-electric machine, more particularly to a rotor of a rotary-electric machine suitable as, for example, a rotor of a turbine generator in which ventilation channels for cooling air are formed in conductors constituting a rotor winding on an end portion of the rotor in an axial direction.
2. Description of the Related Art
A general turbine generator is generally constituted by disposing a rotor supported on a rotation shaft so that the rotor faces a stator. A rotor iron core constituting the rotor extends in an axial direction and has a plurality of slots formed at predetermined intervals in a peripheral direction, and a plurality of conductors forming a rotor winding are laminated and stored in the slots. The conductors are bound by wedges disposed on outer peripheries of the slots, and the wedges are designed so as to hold the conductors even during rotation at a high speed. A retaining ring is fixedly fitted into an end portion of the rotor winding in the axial direction so as to cover the portion via an insulating cylinder, and this retaining ring retains a centrifugal force of the conductors.
Additionally, in general, there is not any distinct channel through which cooling air circulates in the vicinity of the conductors under the retaining ring. Therefore, a temperature of this portion rises, but as a method for preventing the temperature rise of this portion, a method is proposed in which ventilation channels to circulate the cooling air are disposed in the conductors in a longitudinal direction. As shown in, for example, FIG. 9, a ventilation channel 41 through which the cooling air flows is formed on the surface side in a conductor 1 along an axial direction of the conductor and along a peripheral direction halfway. An air inlet hole 21 which communicates with this ventilation channel 41 to introduce the cooling air is disposed in a side surface of the conductor 1. An exhaust hole 51 to exhaust the cooling air which has flowed through the ventilation channel 41 is disposed so as to extend through the conductor 1 in a diametric direction. Furthermore, the cooling air which has flowed through the ventilation channel 41 to cool the conductor 1 is exhausted from an exhaust port 8 formed in a wedge 7 in FIG. 8.
A plurality of the conductors as shown in FIG. 9 are laminated in a multistage manner to constitute the rotor winding, and the cooling air is introduced into the ventilation channels from the air inlet hole formed in the side surface of the rotor winding. After circulating the cooling air through the ventilation channels to cool the rotor winding, the cooling air is exhausted together from the exhaust hole. This is described in JP-A-63-15644.
Moreover, a second air inlet hole of which an opening is formed in the side surface of the conductor is disposed halfway in the ventilation channel to improve a temperature distribution of the conductor in the longitudinal direction. This is described in JP-A-2003-88022.
However, in the above conventional technology (JP-A-63-15644), a temperature of each slot cannot necessarily be lowered efficiently. This will be described with reference to FIGS. 8 and 10. Here, it will be described in accordance with an example of a turbine generator which has a two-pole field system.
The rotor of the turbine generator usually rotates at a high speed such as 3000 or 3600 rotations per minute during a rating operation. At this time, the cooling air for cooling the conductors 1 of the rotor winding is introduced through a gap between a retaining ring 3 and a rotation shaft 2. Here, the cooling air is not introduced in parallel with the axial direction as viewed from the rotor. The cooling air is usually introduced in such a direction that the air has several rotation components. An air inlet angle of the introduced cooling air in such a direction having the rotation components changes with an amount of the cooling air of the rotor, a structure of a stator side, a flow rate of the cooling air on the side of the stator and the like. For example, if the generator has a diameter of 1 m and rotates at a speed of 360° rotations per minute, a rotation speed of the conductor 1 is π×3600/60×1=188 m/s. Supposing that the cooling air does not have any speed in the peripheral direction in a space between a stator 5 and a rotor 4, cooling air 9 has a relative speed of 188 m/s in the peripheral direction as viewed from the rotor 4. Since an axial flow speed of the cooling air in this position is usually about 10 to 20 m/s, the introduced cooling air crosses the axial direction at approximately right angles as viewed from the axial direction.
This is shown in detail in FIG. 10. FIG. 10 is an enlarged view in the vicinity of the conductor 1 in FIG. 8 as viewed from a shaft end, and shows a structure in which a plurality of conductors shown in FIG. 9 are laminated.
In FIG. 10, in the surfaces of conductors 11 to 19, ventilation channels 41 to 49 are formed, respectively. In the side surfaces of the conductors, air inlet holes 21 to 29 are formed which introduce the cooling air into the ventilation channels, respectively. The conductors are turned back at a shaft end portion, and formed into a shape symmetric with respect to a magnetic pole 80.
Usually, an insulating spacer 70 is disposed in a magnetic pole portion in order to restrict movement of the conductors in the axial direction. In a case where a rotating direction is denoted with reference numeral 90, when the cooling air 9 is introduced at a high speed in the peripheral direction as described above, the cooling air 9 does not easily enter the backside (opposite to the rotating direction 90) of the insulating spacer 70. That is, in the example of FIG. 10, when the cooling air 9 blows into at a shown angle, a shaded area 100 is a shadow (backside) of the insulating spacer 70, and the cooling air 9 does not easily enter the backside. That is, there occurs a possibility that a necessary flow rate of the cooling air 9 which enters the air inlet holes 21 to 29 positioned in the shaded area 100 cannot be secured. If the air inlet angle of the cooling air 9 is close to 90°, the cooling air 9 might not flow at all. This also applies to air inlet holes 31 to 39 disposed in positions symmetrical to those of the air inlet holes 21 to 29 with respect to the magnetic pole 80 when the blowing direction of the cooling air 9 changes and the air inlet holes 31 to 39 enter the shadow of the insulating spacer 70. As a result, the temperature is raised without effectively cooling the conductors, and this results in a problem that a cooling performance of the rotor winding is not satisfactory.